Extrusion laminating or coating lines are used to combine an extrudate or coating layer with a material or substrate layer that is being laminated or coated. Conventional extrusion laminating/coating lines use a nip roll or roller that is made from a thermally stable covering in combination with a chilled roll or roller. The extrudate is combined with the substrate that is being coated in the nip area between the nip roll and the chilled roll. In an extrusion process, an extrudate layer is fed on the chilled roll side of the nip area, and the substrate is fed on the nip roll side of the nip area. In a lamination process, a primary layer is fed on the nip roll side of the nip area, a secondary layer is fed on the chilled roll side of the nip area, and the extrudate is fed between the primary and secondary layers. See e.g., U.S. Pat. No. 3,526,000.
Conventional extrusion/coating lines use a nip roll having a thermally stable covering. Typical thermal stable covering used in conventional systems are rubber or rubber like coverings, e.g. synthetic rubbers based on polychloroprene (polymer form of chloroprene), such as Neoprene® by DuPont Performance Elastomers, or synthetic rubbers based on chlorosulfonated polyethylene (CSPE), such as Hypalon® by DuPont Performance Elastomers. The extrudate is typically a thermoplastic material, such as a polymer, e.g. polyethylene, ethylene vinyl acetate (EVA), etc. The thermoplastic material is typically molten when it comes into contact with the substrate in the nip area. If the molten thermoplastic material contacts the roller covering, such as an edge bead, the thermoplastic material will adhere to the roller covering and wrap, thereby causing the production line to stop. To prevent this from occurring, the traditional practice is to apply a Teflon® impregnated tape to the nip roll in the area where the edge bead contacts the roll covering. Conventional tape has an adhesive side opposite the Teflon® impregnated side of the tape, and it is the adhesive side that is applied to the nip roll. This practice works temporarily, but when the release properties of the tape are no longer sufficient or the tape has burned through due to the heat of the thermoplastic material, the hot material will adhere to the roller covering causing a nip wrap that requires the line to shutdown. Also, whenever the width being run changes, the tape position needs to be changed, thereby requiring the line to be shutdown so that the tape can be removed and new tape applied to the surface of the nip roll. Conventional Teflon®/adhesive tape systems are time consuming to apply, expensive and not very durable.
Another conventional approach to reduce nip wraps is to apply a Teflon®-sleeve around the entire nip roll. Teflon®-sleeved rollers, however, are costly and are very susceptible to damage due to their lack of resiliency and durability.
Another conventional approach to reduce nip wraps is to use a pre-assembled Teflon® belt having a cloth backing. Conventional pre-assembled Teflon®/cloth backing belt systems are time consuming to apply, expensive and not very durable. These conventional pre-assembled belt systems require machine disassembly for installing the pre-assembled belt on the nip roll of an extrusion laminator. Also, the thickness of the belt, due to the cloth backing, can cause grooves to be worn into the surface of the nip roll. If the position of the tape is incorrect and the extrudate contacts the nip roll, then a nip wrap can result.
All three of the approaches described above fail to provide a cost effective approach as the downtime associated with nip wraps remains significant.